Vacuum electric tube device



March 27, 1 928.

. E. Y. ROBINSON ET AL VACUUM ELECTRIC TUBE DEVICE Filed Sept. 27, 1924 llAllllllA VIVIIIIIVI INVEN OR 5 Ernest Jeo nfobmson d h/d/teYL/a/lfl Bro wn ATTORNEY WITNESSES: W7

Patented Mar. 27, 1928.

Banner xnoivmiv nonrlvsom OF MIANGHESTER,LAND!WALTER U'OHNiBROMENJQFJSTOGK PERT}, ENGLAND; ASSIG-NORS-L TO "METCRQPOLIEANRVIGKERSE E-LE GTBICJALL- COM- VACUUM ELEGTRIC TUBE DEVICE.

Application filed September 27, 1924, .Serial No. 740,150, andvin G-reat Britain 0ctober'8,11928.

This invention relates to. vacuum electric tube devices of the hot cathode-type and has for its object" to provide automatic means Whereby'in the event of the cathode such as .a filament of'a valve being. burnt-out during operation another cathode Will be-brought into operation in place thereof.""T-lie other cathode may 'be located in the valve in "which case the same valve' will continue inservice; oran. auxiliary valve may'be' used and Tsimilarly brought into service. Aiurtherobject is .toiprovide automatic means of lthe above indicated 'ch'arac'ter whereby when, upon the failureof a cathode, anothercoathode or valve is brought into operation, practically n'ofinterrupti'on 70f service willfitakejplace and the resulting disturbance willbe small or negligible. a

In order that no appreciable interruption of service and only a negligible disturbance shall take place it; is essential that :the anode current and consequently the-electronfemission should not fall below a certain value Whilst'th'e automatic changeover is taking place. The anode of the second or auxiliary valve, When such is employed, may obviously be connected {permanently toa source of potential and-the grid "thereofmay be like- Wise permanently connected to an input circuit but ifthe cathode of saidjvalveis .cold before being brought into operatiomaniinterval of time mustelapse before the'said cathode attains its normal vvorking temper ature whereby anappreciable interruption oi'the anode current'must'occur. Now it is-well known that the electron'emission'of a'heated cathodeand the evaporationthereof changes comparatively rapidly "with variations of temperature and "thatthere is it'or a given cathode material aitemp'erature above which evaporation and'electronic emission takes place freely Whilst below said temperature the evaporation and iemissi'on is negligible which may be defined as the critical temperature.

According to the-invention. the-second or spare cathode or the cathode of the auxiliary valve is normally maintained at a relatively high stand-by temperature fvvhich is just below the critical temperature for electron emission and means governed "by-the operativeness of the main cathode are provided for automatically increasing th'e'tempe-rature of said-second or spare cathode above the critical temperature thereof When-the main cathodeburns out'or becomes inoperative. In'thismanner the. interruptionndue 'to the substitution oflithe; new cathode for the original one and the consequent'di'sturbance is small and may'in'some cases?be negligible. 0

' The automatic increasmof the temperature oi? "the-second or' spare? cathode may' be -*e'f-' fected in various Ways but according to a furtherfeature of the iIlVGlltiOn'ftlliS is -ef fected Without the use ofswitchingxdevices in'a'manner tobehereiria'ftrdescribed! A relay or other electrically operated device may be included in :thesystem and so controlled in accordance with :the 'operativene'ss of the valves zasftooperate "an indicator or warning signal- "when the cathode-burns out.

Furthermore the electrodes=suchas the anodeand gric'l of thesecond or spare'valve 'Whensuch 15 used may be permanently con valve as "previously "herein stated; or alternativ'ely#theykmay "be connected by "means of automatic switches immediately on 'fai'lure of "the mainvalve, and"iaccording to an:-

other feature such electrodes offthelmain valvemay clisconnec'ted by. automatic sw tching. devices when the changeover "is effected: :Such .autom'ati'c "switchin devices may be controlled'forexample by'ich'anges trating aniainhand an auxilia valve 'together "with .anautomatic .switc' for-their .anodeand *grid' -circuits; Fig.2 is an electrical diagram of'ias-main" and I an" auxiliary valve arranged to operate without the syvitc'hin'g means, and Fig. 3 isaumodifica tron: of this arrangement. 'fFigfli is .a m'odi- :fic'ation .ofthe invention employing a single tube 'with two cathodes.

Referring "coFi'g; l "the main valve. is

shown by 1" and the lauxiliary valve.by ;2.

The automatic switchfor-efi'ecting'the alternative --connections o'fzithetwo valves is shown by; 3. The cathode supply current is 1 obtained from the terminals i land 5. The

cathode dofthe valve 1 is connected across the supply terminals through the. operatiii g coil 17 "of the automatic switch, and the oathode 8 o'fthe valve 2 is similarly connected across the terminals 4-. and 5 throu-gha resistance 9.

The automatic switch 3 is of the 6-pole two-way type. and comprises a plurality of pivoted switch arms 10 to inclusive which are adapted to engage respectively with the contact segments 16 to 21 inclusive. The switch arms are all linked toa rod '22 and are thereby adapted to be operated simultaneouslyi The switchfis biased to one'ot' 2 its two'operative positions by means of a Spring 23 attached to, a rigid support 24-. A'magnetizable member (not shown in the drawing) is provided on the switch to cooperate with the coil' 7. The contact segments of the switch are so arranged that the switch arms 12, 13, 14. and15 are out'ol engagement with their corresponding. segments when the switch arms 10 and 11 are engaged, and vice versa. The anode '25 of the valve 1. is connected to the contact segment16 and thegrid 26 to the'segment 17. Similarly the anode 27 of the valve 2 is connected to the contact segment 18 and the grid 28 to the segment 19. The switch arms 10 and, 12 are connected to the anode supply terminal 29 and the switch arms 11 and 13 to the grid supply terminal 30. lhe switch ariii 14E is connected to one terminal of the resistancefl and itscorresponding contact segment 20-is connected to the other terminal of resistance 9. The switch arm 15 is connected to its corresponding contact segment 21 through a warning device 31, such as an electric bell, and an opea-at-ing battery -32-tor the hell. 7

When the arrangement is in operation the values or the resistance 9 and o'lit-he voltage applied across the terminals t and 5 are adjusted so that the cathode 6 of thevalve 1 is at its normal operating temperature, while the cathode 8 of the valve 2'is at the maximum permissible ten'iperature below its normal operating te1hperature such that evaporation of the cathode is negligible. The operating coil"? of the switch 3 is then energized, and by means or" its cooperating magnetic member maintains the switch in one'operative position against the action of the biasing spring 23. That is to say, the switch arms 10 and 11 alone make contact with their corresponding segments. When the cathode 6 of the valve 1 burns out the switch operating coil 7 is deenergized and the switch-is pulled into its other operative positions through the action of the spring 23. That is to say, the switch arms 12, 13, 14:, and 15 then engage their corresponding contact segments. The anode and grid supplies are thereby switched from the valve 1 to the valve 2, the resistance 9 is short-circuited to bring the temperature of the cathode 8 or the valve 2 to its normal operative value, and the electric warning bell 31 is rung.

In Fig. 2 an arrangement'is illustrated in which the changeover from the mainvalve 1 to the auxiliary valve 2 on failure of the main valve cathode is effected without switching means. In this arrangement the cathode current supply is obtained from the terminals 4 and 5, and the cathode 6 is connected in series with the resistance 33 across the terminals 4 and 5 whilethe cathode 8 of the valve 2is connected in series with the resistance 34 in parallel with the cathode 6 ol the valve 1. The anodes 25 and27 of the valves 1 and'2 respectively may both be connected directly to the anode supply terminal 29 and the grids 26 and 28 connected to the grid supply terminal 30. I

A relay may be included in the circuit and arranged to operate an indicator or warning signal when the current through it decreases owing to one of-the' filaments being burnt out, or the said-relay may be arranged in series with the filament and arranged to operate when the current ceases to flow there-1 through owing to the filament being burnt out. Instead of a separate warning signal or indicator the bulb of the spare valve may be coloured or placed behind a coloured screen to give visual warning when the changeover from valve 1 to valve 2 takes place. I I

Alternatively the arrangement shown in this modification of the invention can-be as sociated if "desired with the switching means described withreference to Fig.1. Also in a further modification a single Valve can be provided with a plurality of auxiliary cathodes which can' be maintained at temperatures below their normal operating temperature and successively switched into or other wiseincludedin the main circuits on failure of the successive main cathode.

In'the operation of the arrangement of Fig. 2 the values of the main resistances 33 and 34. and of thejvoltage applied across the terminals 4L and 5 are adjusted, so that the cathode-6 of the main valve 1 is maintained at its normal operating temperature while the cathode 8 of the auxiliary valve 2 is maintained at a temperature below its norinal operating temperature such that emission and evaporation of thefcathode is negligible. w

The correct values vfor the resistances 33 and 34 and for the electromotiveforce applied between the terminals 4 and 5 can be found experimentally, or alternatively can be calculated from the formulae obtained by the following mathematical analysis.

WVhen the arrangement shown in Fig. 2 is in operation let E represent the value of the voltage applied across the terminals 4 and 5, and X and Y represent the respective values of the resistances33 and 34, which have to be calculated. Let I; represent the known value of the cathode current in the main E=E1+X(I1+I,) 1

E1=E2+I2Y 2 WVhen the cathode of valve 1 burns out the current through the cathode of valve 2 must be increased from I to 1,. Therefore the following new equation then holds for valve 2- E=E +I (X+Y) 3) It follows from equation (2) that from equations (1) and (3) that l 1 1( 1 2) T and from equations (1) and (5) that- L Lagg a 6) 2 Since the numerical values of I and E I and E are known the appropriate numerical values of Y, X and E can be calculated from equations (4), (5) and (6) respectively.

In the arrangement described with reference to Fig. 2 it is necessary to replace a burnt out main valve 1 by a new one which automatically takes up the load. Thus the auxiliary valve 2 is brought into operation at each failure of the main valve 1 and is never replaced. In time it naturally fails also and no automatic operation of the arrangement is then possible. In order to avoid this difliculty the modification shown in Fig. 3 can be employed. In this arrangement one terminal of each of the cathodes 6 and 8 is connected to the cathode current supply-terminal 4. The other two cathode terminals are connected together through the resistance 35 and are also connected respectively through resistances 36 and 37 to the contacts 38 and 39 of a two-way switch 40. The switch 40 is provided with an operating arm 41 which is connected to the cathode current supply terminal 5 and can be operated either manually or electrically from an auxiliary circuit. The anode and grid terminals of the valves can be connected directly to their corresponding supply terminals or alternatively can be associated with a switching device such as is described with reference to Fig. 1. Also suitable warning devices can be provided.

When the switch arm 41 engages with contacts 38 the arrangement of Fig. 2 is exactly reproduced, that is to say, the valve 1 is the main valve and valve 2 auxiliary. When the switch arm 41 engages with the contact 39 the valve 2 becomes the main valve and valve 1 auxiliary. Thus by changing over the switch arm 41 each time a failure occurs the load between the two valves can be evenly distributed and the replacement of each one in turn assured.

It is to'be understood that variousmodifications can be made in the arrangements described without departing from the scope of the invention.

We claim as our invention 1. In a vacuum-tube device, a plurality of cathodes, means for maintaining one of said cathodes at a temperature so high that it will render the device operative, and means for maintaining another cathode at a temperature belowthat required to render the device operative, said last named temperature being so high that the time required to raise said other cathode toa temperature which will render the device operative is too short to noticeably interrupt the operation of the device.

2. In a vacuum-tube device, two cathodes 1n parallel and a resistance in serles with only one'of saidcathodes, said resistance being sufiicient to keep the current through its cathode below the value necessary to produce,

an effective electron emission from said cathode and insufficient to prevent said current reaching said value when the circuit through the other cathode is open. 7

3. In a vacuum-tube device two cathodes,

a source of heating current for said cathodes,

means for so proportioning the current from said source that one cathode is above, and the other below the temperature which is just sufficient to render the vacuum-tube device operative, said proportioning means admitting sufficient current to the cooler cathode to heat it nearly to said temperature and upon failure of the hotter cathode admitting additional current to the other cathode.

4. In a vacuum-tube device, a pair of vacuum tubes, a cathode in each vacuum tube, a source of heating current common to said cathodes, a resistance connected between said cathodes, a pair of resistances connected on opposite sides of said resistance, and a switch for connecting either member of said pair of resistances in series with said source.

ERNEST YEOMAN ROBINSON. WALTER JOHN BROWN. 

